Hitherto, a laser processing device for processing an object to be processed by using laser light emitted from a laser oscillator has been well known (see, for example, Patent Literature 1).
FIG. 7 is a block diagram schematically illustrating an optical path configuration of a related-art laser processing device described in Patent Literature 1.
In FIG. 7, laser light L generated from a laser oscillator 1 is transmitted to a processing lens (not shown) in a processing head 4 via a transmission optical system to be condensed and radiated to an object to be processed (not shown) placed on a processing table 2.
The processing table 2 and the processing head 4 include moving means 5 capable of moving each of the processing table 2 and the processing head 4 in at least one axial direction. The moving means 5 can move a relative position between the laser light L and the object to be processed in a desired direction and can locate the relative position at a desired position.
In this case, the moving means 5 is configured to move the processing table 2 in an X axis direction and to move the processing head 4 in a Y axis direction.
The transmission optical system for the laser light L includes a reflective beam expander mechanism 106 that the laser light L from the laser oscillator 1 enters, and a reflection mirror 8 for introducing the laser light L emitted from the reflective beam expander mechanism 106 into the processing head 4.
The reflective beam expander mechanism 106 includes a reflection mirror 68 that the laser light L from the laser oscillator 1 enters, a spherical convex mirror 63 that the laser light L reflected by the reflection mirror 68 enters, and a spherical concave mirror 65 that the laser light L reflected by the spherical convex mirror 63 enters.
The reflective beam expander mechanism 106 increases a beam diameter of the laser light L by a desired scaling factor irrespective of a divergence angle of the laser light L generated from the laser oscillator 1, and maintains an appropriate condensed light diameter at a processing point on the processing table 2.
It is known that, generally, astigmatism in accordance with an incident angle occurs in light reflected by a spherical mirror such as the spherical convex mirror 63 or the spherical concave mirror 65. In particular, when astigmatism occurs in the laser light L in a laser processing device, the light condensation ability is reduced and the beam shape becomes anisotropic at the processing point.
In this way, in a laser processing device of a type in which the processing head 4 moves, the reflective beam expander mechanism 106 for magnifying and collimating the laser light L is provided in the optical path in order to maintain an appropriate condensed light diameter at the processing point of the object to be processed. When a spherical mirror is used in the reflective beam expander mechanism 106, in order to inhibit astigmatism, it is necessary to restrict the incident angle with respect to the spherical mirror to an acute angle.
Therefore, when a spherical mirror is used in the transmission optical system of the laser processing device, in order to avoid lowering of processing quality and occurrence of anisotropy in processing due to astigmatism, it is necessary to restrict the incident angle of the laser light L with respect to the spherical mirror to an acute angle so that the astigmatism does not adversely affect the processing quality.
It is known that, generally, when the incident angle with respect to the spherical mirror is set to be an acute angle (desirably 15° or less), lowering of the processing quality due to astigmatism is negligible.
Therefore, in FIG. 7 (Patent Literature 1), the reflection mirror 68 in the reflective beam expander mechanism 106 restricts incident angles of the laser light L with respect to the spherical mirrors (spherical convex mirror 63 and spherical concave mirror 65) to acute angles, respectively.
However, when the reflection mirror 68 for restricting the incident angles with respect to the spherical mirrors is provided, the optical path is complicated, and further, in a strict sense, the astigmatism cannot be inhibited. Further, through absorption of the laser light by optical elements in the complicated optical path, the thermal lens effect is produced, and thus increase in the number of the optical elements is a factor of processing instability.